— Four hundred years ago, Galileo Galilei changed the world by peering through a 3-foot-long telescope and spying the moons of Jupiter. Today, the world — or, more accurately, our collection of worlds — is on the brink of a change that could be just as dramatic.
Over the next five years, giant telescopes and far-seeing space probes will revolutionize the way we think of stars, planets and the other denizens of planetary systems, including our own.
One of the planetary pioneers is NASA's Wide-Field Infrared Survey Explorer, launching next week from Vandenberg Air Force Base in California. WISE is designed to look for objects too dim and distant to be noticed by past probes. By mid-2011, the polar-orbiting satellite should detect around 100,000 previously unseen asteroids. Even more intriguingly, the satellite has a chance of spotting a brown-dwarf star or a new planet on the outskirts of the solar system.
"There is still the possibility of a large planet in the outer solar system, according to some experts," the mission's project scientist, Peter Eisenhardt of NASA's Jet Propulsion Laboratory, told msnbc.com. "My point of view is, as long as there's a reasonable chance of finding something, you ought to go and look."
Looking beyond our solar system, astronomers are gearing up to reveal the initial findings from NASA's Kepler mission next month. Kepler is aimed at determining how many stars in a patch of sky have planets circling around them. Within three years, scientists hope to be able to detect Earth-size planets in the "habitable zones" around alien stars.
After only a few months of observations, leaders of the Kepler team say they've already come across some potentially mind-bending findings. "We have some discoveries that someday, after they're verified, will knock your socks off," the mission's principal investigator, William Borucki of NASA's Ames Research Center, told msnbc.com.
Another planet-hunting probe, the European Space Agency's COROT satellite, has already detected a rocky world only five times as massive as Earth, orbiting so close to its parent star that temperatures on the sun-facing side rise beyond 2,000 degrees Fahrenheit. Still more planets are sure to be revealed in the months and perhaps years to come.
Ground-based telescopes are joining the search for new worlds as well. Some of the world's biggest eyes on the sky are already supporting the Kepler and COROT missions, and still more are in the design or construction phase:
Lowell Observatory was the place where Pluto was discovered back in 1930, and observatory director Eileen Friel said it's fitting that the one of the first campaigns taken on by the new telescope will be to look for other objects like Pluto in the Kuiper Belt. "It has direct relevance to the observatory's legacy," she told msnbc.com.
That legacy has undergone substantial revision in the past three years: Pluto is no longer considered the ninth planet, but rather the first of many ice dwarfs that could be identified in the Kuiper Belt. The dwarf-planet population already includes Eris, a world even bigger than Pluto that was found almost five years ago.
Eris' discovery led the International Astronomical Union to come up with the definition for a dwarf planet in 2006, and move Pluto from the list of planets proper to the new classification.
Some astronomers continue to debate Pluto's demotion, but however the planetary pigeonholes are reshuffled, Pluto is due for a fresh look in 2015 when NASA's New Horizons probe sails by. Past studies have already determined that Pluto has a thin atmosphere, as well as clouds and weather patterns. Pluto's biggest moon, Charon, shows hints of having ice volcanoes, and Pluto may exhibit similar geological activity.
New Horizons' observations could flesh out all those hints and present the public with a new, more planetlike image of Pluto and its kin. Another probe, NASA's Dawn spacecraft, may do the same for the solar system's smallest known dwarf planet, the asteroid Ceres, when it begins its reconnaissance mission in 2015.
Vanderbilt University astronomer David Weintraub said Pluto and Ceres "will take on a new life when we see them as real objects." The new wave of world hunters could spark a similar transformation in the concepts of stars and planets, inside and outside our solar system.
Is there a big Planet X out there?
WISE, for example, is designed to scour areas that have not been looked at closely by past probes, far above and below the ecliptic plane, where the solar system's eight largest planets make their orbits. Because the probe searches in mid-infrared wavelengths, it could pick up objects that are too dim to be detected by their visible light.
"We're sensitive to objects that are as cold as 50 Kelvin," or 370 degrees below zero Fahrenheit, Eisenhardt said. "That means objects that are way, way out there in the farther reaches of the solar system."
He said WISE isn't the best instrument for detecting dwarf planets such as Pluto or Eris, but it should be able to pick up larger planets or brown dwarfs that couldn't be seen before. A world the size of Neptune could be spotted in an orbit 50 times farther away than Pluto's distance from the sun. Something as big as Jupiter could be seen even if it were a light-year away — more than 1,000 times farther than Pluto.
In some quarters, such a discovery could lead to hand-wringing over a Planet X that's out to get us, but the researchers who have hypothesized the existence of such a planet emphasize that orbital mechanics would rule out any threat. And if WISE fails to detect a large planet, that should deal a mortal blow to the Planet X hypothesis, said John Matese, an astrophysicist at the University of Louisiana at Lafayette who has studied the issue for years.
"If it doesn't discover it, the whole discussion should be concluded," he said.
Looking for ‘failed stars’
WISE's science team is more confident about detecting brown dwarfs, which are sometimes known as "failed stars." Brown dwarfs are celestial bodies big enough to get a deuterium fusion process started — with masses higher than 13 times Jupiter's mass — but too small to sustain the hydrogen fusion reaction seen in stars.
Brown dwarfs glow so dimly that they're difficult to detect, but when astronomers study distant star clusters closely, they usually spot at least one brown dwarf for every regular star. Astronomers suspect that our own celestial neighborhood contains brown dwarfs that have not yet been spotted. Some could be wandering closer to the solar system than our nearest known stellar neighbor, Proxima Centauri, which is 4.2 light-years away.
"We should find several hundred brown dwarfs that are currently unknown," Ned Wright, an astrophysicist at the University of California at Los Angeles who serves as WISE's principal investigator, said in a news release.
Some of those dark stars could even have planets, Wright said, and the yet-to-be-launched James Webb Space Telescope could focus on targets identified by WISE to look for them.
Over the course of its planned nine-month science mission, WISE is expected to boost the solar system's inventory of asteroids by 100,000, Eisenhardt said. A system is being put in place to report hundreds of new asteroids per day, and to follow up on WISE's avalanche of data with ground-based telescope observations.
Fresh discoveries, from WISE as well as other observational campaigns in space and on Earth, have the potential to blur the lines even further between stars, planets (from giants to dwarfs) and even smaller objects such as asteroids and comets. When astronomers want to study the entire planetary spectrum, they currently have only one sample to look at: our own solar system. And even there, scientists still haven't seen the full sample.
Now that's about to change, and the reshaping of planetary science — a process that started in earnest five years ago with the discovery of Eris and the reclassification of Pluto — could continue for a long, long time. "We expect that the legacy of the WISE survey will last for decades," Eisenhardt said.